In the case of minerals we find such critical stages at the melting and boiling points, for example, when the solid suddenly becomes a liquid or the liquid becomes a gas.

In the case of plants we see such critical stages when the seed begins to germinate, or the bud bursts into leaf.

In the animal world we see the same on every hand, as when the grub suddenly changes into a butterfly, the chick emerges from its shell, or the babe is born from its mother's womb.

In the higher life of the soul we often see a similar transformation, when a man is "born again" and his whole being becomes radically changes in its aims, its character and activities.

Such critical stages often affect a whole species or multitude of species simultaneously, as when vegetation of all kinds suddenly bursts into new life in springtime.
Baha'u'llah declares that just as lesser living things have times of sudden emergence into new and fuller life, so for mankind also a "critical stage," a time of "rebirth," is at hand.